Function Of External Electric Field Research Articles

New method to measure domain-wall motion contribution to piezoelectricity: the case of PbZr0.65Ti0.35O3 ferroelectric

A new data analysis routine is introduced to reconstruct the change in lattice parameters in individual ferroelastic domains and the role of domain-wall motion in the piezoelectric effect. Using special electronics for the synchronization of a PILATUS X-ray area detector with a voltage signal generator, the X-ray diffraction intensity distribution was measured around seven split Bragg peaks as a function of external electric field. The new data analysis algorithm allows the calculation of `extrinsic' (related to domain-wall motion) and `intrinsic' (related to the change in lattice parameters) contributions to the electric-field-induced deformation. Compared with previously existing approaches, the new method benefits from the availability of a three-dimensional diffraction intensity distribution, which enables the separation of Bragg peaks diffracted from differently oriented domain sets. The new technique is applied to calculate the extrinsic and intrinsic contributions to the piezoelectricity in a single crystal of the ferroelectric PbZr1−x Ti x O3 (x = 0.35). The root-mean-square value of the piezoelectric coefficient was obtained as 112 pC N−1. The contribution of the domain-wall motion is estimated as 99 pC N−1. The contribution of electric-field-induced changes to the lattice parameters averaged over all the domains is 71 pC N−1. The equivalent value corresponding to the change in lattice parameters in individual domains may reach up to 189 pC N−1.

Improvement of electrocaloric properties of P(VDF-HFP)/GNPs composites for refrigerator cooling

Electrocaloric effect originally comes from the cross-coupling between temperature and polarization of dielectric materials. Poly (vinylidene fluoride)/P(VDF) and its copolymers exhibit high displacement and dielectric properties among all ferroelectric polymers with additional advantages like lightweight, flexible and low cost compared with other dielectric materials. Moreover, poly (vinylidene fluoride hexafluoroprophylene)/P(VDF-HFP) copolymers shows highest breakdown strength. P(VDF-HFP) copolymers was used as the main matrix with graphene nanoplatelets (GNPs) conducting materials as nanofillers. The P/GNPs composites thin films were prepared by solution casting method with the final thickness of 30 +/- 5 µm using N, N-dimethylformamide (DMF) as solvents. The GNPs content was varied of 0, 1, 2, 3, 4 and 5% by weight. The dielectric and electrical properties were measured by LCR meter with various frequency of 1 to 100 kHz. The structure and crystallinity were observed by XRD and DSC. The polarization as a function of external electric field was investigated by P-E loop instrument in 40 MV/m with varying temperature from room temperature to 140 °C. Furthermore, electrocaloric effect was measured by indirect method by calculating adiabatic temperature change (ΔT) with help of Maxwell relation. The experimental results show that dielectric constant of P/GNPs composites was increased by increasing the GNPs content but dielectric loss is kept constant with low loading, far away from the percolation threshold. Moreover, the ΔT of the P/GNPs composites is higher than the pure P(VDF-HFP) copolymers that leads to higher electrocaloric effect. The Increasement of the ΔT of P/GNPs composites will be discussed based on their microstructure, phase transition and crystallinity. As conclusion, adding GNPs nanofillers to P(VDF-HFP) matrix can improve dielectric constant as well as electrocaloric properties which has capability for refrigeration cooling system.

Oscillation of Electron Mobility in V‐Shaped Double Quantum Well Structure Under Applied Electric Field

Herein, it is shown that the oscillation of low temperature electron mobility μ can be obtained as a function of external electric field F in AlxGa1−xAs based V‐shaped double quantum well (VQW) structure. The oscillation of μ can be enhanced by increasing the well width and barrier width as well as decreasing the doping concentration and height of the V‐shaped potential. The mobility due to the ionized impurity (II‐) scattering μII is responsible for the oscillation of μ through intersubband effects within double subband occupancy. On the other hand, the mobility due to the alloy disorder (AD‐) scattering, μAD, which shows almost a flat‐like character, governs the overall magnitude of μ. It is further gratifying to show that the drop in μ at the transition from single to double subband occupancy minimizes and even alters to a rise in μ by varying the AD‐scattering potential through the structure parameters of the VQW. These results can be utilized to analyze the non‐square quantum well based field effect transistors.

Strain-Mediated Converse Magnetoelectric Coupling in La0.7Sr0.3MnO3/Pb(Mg1/3Nb2/3)O3–PbTiO3 Multiferroic Heterostructures

The converse magnetoelectric (ME) coupling of a La0.7Sr0.3MnO3 (LSMO) thin film, deposited on piezoelectric Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN–PT) single crystal substrate by the pulsed laser deposition (PLD) technique, was investigated by magneto-optical Kerr effect (MOKE) system. Because of the piezoelectric nature of the PMN–PT, the strain status of the LSMO thin film is tunable by the electric field applied on the substrate, as it is well-known that the Manganite thin film has very strong electron–phonon interaction; thus, the magnetic property change as a function of external electric field can be realized. The change of the Kerr signal of LSMO film upon applying direct current (DC) voltage to the PMN–PT single crystal was recorded. In particular, the voltage-induced change of the Kerr signal in the LSMO by applying the alternative current (AC) actuation voltage bias to the PMN–PT single crystal can be in situ recorded without external magnetic fields. The gained Kerr signal versus voltage loop basically t...

In-situ X-ray diffraction on functional thin films using a laboratory source during electrical biasing

A methodology that allows the quantification of structural changes in functional thin films during the application of external electrical field is reported. The originality of this method is the development of a set-up using a laboratory X-ray source since most of previous Operando studies have used synchrotron radiations. Several technical challenges have been addressed: the (i) optimization of the electrical contact and the sample geometry within the lab-source goniometers, (ii) evaluation of any X-ray dose effect on the Metal/Insulator/Metal structure to prevent eventual charge accumulation at the electrode interfaces and (iii) the quantification of the effect of the time-delay, needed for X-ray measurement, on domain switching. The validity of our method has been demonstrated on a prototypic sol-gel lead zirconate titanate (PZT) thin film where the polarization and structural changes have been simultaneously measured. The evolution of ferroelastic domains as a function of external electric field has been quantified and two different effects have been successfully separated: (a) the cell extension and (b) domain wall motion described as the switching between a and c tetragonal domains.

Tuning the Schottky contacts at the graphene/WS2 interface by electric field

Evolution of Schottky barriers of ΦBp and ΦBn in graphene/WS2 heterostructures as a function of external electric field.

Electric control of inverted gap and hybridization gap in type-II InAs/GaSb quantum wells

The quantum spin Hall effect has been predicted theoretically and observed experimentally in InAs/GaSb quantum wells as a result of inverted band structures, for which electron bands in InAs layers are below heavy hole bands in GaSb layers in energy. The hybridization between electron bands and heavy hole bands leads to a hybridization gap away from k=0. A recent puzzling observation in experiments is that when the system is tuned to more inverted regime by a gate voltage (a larger inverted gap at k=0), the hybridization gap decreases. Motivated by this experiment, we explore the dependence of hybridization gap as a function of external electric fields based on the eight-band Kane model. We identify two regimes when varying electric fields: (1) both inverted and hybridization gaps increase and (2) inverted gap increases while hybridization gap decreases. Based on the effective model, we find that light-hole bands in GaSb layers play an important role in determining hybridization gap. In addition, a large external electric field can induce a strong Rashba splitting and also influence hybridization gap.

Work function change of Ni, HfO2films and Ni/HfO2interfaces as a function of external electric field

In this paper, the effects of external electric field on the work functions for Ni(001), Ni(111), HfO2(001) and HfO2(111) films and the effective work functions for Ni(001)/HfO2(001) and Ni(111)/HfO2(111) interfaces were studied by first-principles methods based on density functional theory (DFT). It is found that the work functions for all the systems change linearly with the strength of external electric field. Comparing the slopes of the work function variation versus external electric field strength for Ni, HfO2films and Ni/HfO2interfaces, we have found that the response of the effective work function to external electric field for Ni/HfO2interfaces is determined by the response of the HfO2side to external electric field.

Magnetic properties of Dirac fermions in a buckled honeycomb lattice

We calculate the magnetic response of a buckled honeycomb lattice with intrinsic spin-orbit coupling (such as silicene) which supports valley-spin polarized energy bands when subjected to a perpendicular electric field $E_z$. By changing the magnitude of the external electric field, the size of the two band gaps involved can be tuned, and a transition from a topological insulator (TI) to a trivial band insulator (BI) is induced as one of the gaps becomes zero, and the system enters a valley-spin polarized metallic state (VSPM). In an external magnetic field ($B$), a distinct signature of the transition is seen in the derivative of the magnetization with respect to chemical potential ($\mu$) which gives the quantization of the Hall plateaus through the Streda relation. When plotted as a function of the external electric field, the magnetization has an abrupt change in slope at its minimum which signals the VSPM state. The magnetic susceptibility ($\chi$) shows jumps as a function of $\mu$ when a band gap is crossed which provides a measure of the gaps' variation as a function of external electric field. Alternatively, at fixed $\mu$, the susceptibility displays an increasingly large diamagnetic response as the electric field approaches the critical value of the VSPM phase. In the VSPM state, magnetic oscillations exist for any value of chemical potential while for the TI, and BI state, $\mu$ must be larger than the minimum gap in the system. When $\mu$ is larger than both gaps, there are two fundamental cyclotron frequencies (which can also be tuned by $E_z$) involved in the de-Haas van-Alphen oscillations which are close in magnitude. This causes a prominent beating pattern to emerge.

Hot-electron noise properties of graphene-like systems

We study the hot-electron noise properties of two-dimensional materials with a graphene-like energy dispersion under a strong applied electric field which drives the system far from equilibrium. Calculations are based on a Boltzmann--Green-function method within a two-relaxation-time approximation that allows for both inelastic scattering coming from electron-phonon scattering and elastic scattering coming from electron-impurity scattering. The steady-state distribution function is used to calculate the average current and the low-frequency spectral density for current fluctuations (noise) in the nonequilibrium steady-state. We find that as the electric field strength increases, the noise decreases from its equilibrium thermal noise value. This is in contrast with semiconductors with a quadratic energy--wave-vector dispersion where the noise increases in a constant-relaxation-time model with the square of the electric field due to the Joule heating of the electron gas by the electric field. We have also studied these properties for an electronic dispersion with a gap introduced into the Dirac spectrum. The inclusion of the gap in the electronic dispersion causes an initial increase in the noise as a function of external electric field due to the heating of the electron gas for large gap values. At high electric fields, the noise decreases with increasing electric field as in the case of gapless dispersion at higher fields.

The influence of photosensitizers on the photorefractivity in poly[methyl-3-(9-carbazolyl)propylsiloxane]-based composites

We investigated the photosensitizers effect on the photorefractive (PR) properties in five poly[methyl-3-(9-carbazolyl)propylsiloxane] (PSX-Cz)-based PR composites which were doped with various photosensitizers having each different electron affinity, such as 2,4,5,7-tetranitro-9H-fluorine-9yilden malonitrile (TeNFM), 2,4,7-trinitro-9-fluorenone (TNF), 9-dicyanomethylene-2,4,7-trinitro-fluorenone (TNFM), tetracyanoethylene (TCNE), and 7,7,8,8-tetracyanoquinnodimethane (TCNQ). At 632.8 nm, photo-charge generation efficiencies, photoconductivities, space charge field, four wave mixing diffraction efficiencies, and PR grating buildup times were measured as a function of external electric field. The photo-charge generation, which is dependent on the light absorption, was achieved through the charge transfer (CT) complexes between the PSX-Cz and each of the photosensitizers. The photon energy of the CT transition decreased with increasing electron affinity of the photosensitizer. In composites doped with TeNFM, TNF, and TNFM, the space charge field ( E sc) increased as the photo-charge generation efficiency increased; the grating buildup in these composites is rate-limited by the photo-charge generation speed. In sample doped with TCNE, and TCNQ, the hole mobility was reduced due to the larger amount of photosensitizer anion traps produced by photoreduction of the photosensitizer. Then, the grating buildup speed became hole mobility limited, and smaller buildup rates were observed. The magnitude of space charge field was sustained as the charge and trap density increased. In all composites, the refractive index modulation is increased with the magnitude of space charge field.

Feasibility of a storage ring for polar molecules in strong-field-seeking states

We show, through modeling and simulation, that it is feasible to construct a storage ring that will store dense bunches of strong-field-seeking polar molecules at 30 m/s (kinetic energy of 2 K) and hold them, for several minutes, against losses due to defocusing, oscillations, and diffusion. The ring, 3 m in diameter, has straight sections that afford access to the stored molecules and a lattice structure that may be adapted for evaporative cooling. Simulation is done using a newly-developed code that tracks the particles, in time, through 400 turns; it accounts for longitudinal velocity changes as a function of external electric field, focusing and deflection nonlinearities, and the effects of gravity. An injector, decelerator, and source are included and intensities are calculated.

Change of Work Function of Pd, Ag, K on Al(001) as a Functionof External Electric Field

We present a local density functional calculation of the effect of anexternal electric field on the work function change of Pd and Ag adsorptionon an Al(001) surface. The adsorption of K has also been considered forcomparison. We found that the work functions for all the systems increasedlinearly when the strength of the external electric field was increased. Sincethe polarized electrons at the interstitial regions between the adsorbateand substrate for Pd/Al(001) and Ag/Al(001) react to the external electricfield differently, the subtle differences between Pd/Al(001) and Ag/Al(001)bondings has been characterized through the comparison of the slopes of the workfunction change versus electric field.

Wall velocities, switching times, and the stabilization mechanism of 180° domains in congruent LiTaO3 crystals

A systematic study of the kinetics of 180° domains as a function of external electric field is presented for Z-cut LiTaO3 single crystal wafers at room temperature using transient current measurements combined with nondestructive and real-time imaging of 180° domains by light microscopy. The switching time, wall velocity, and nucleation rate follow an exponential behavior with the applied field. A model is proposed which shows that the nucleation and sideways growth of domains play approximately equal parts in determining the switching time. A domain stabilization process occurs on the time scale of a few seconds even at electric fields where the switching time is milliseconds or less. We show that this stabilization process has a strong correlation to the internal fields in the crystal.

The effect of electric field on the excitonic states in coupled quantum well structures

We have calculated by a variational procedure the excitonic states in symmetric coupled quantum well structures of GaAs/AlGaAs in the presence of an external electric field perpendicular to the interfacial plane using a nonseparable, nonspherical hydrogenic trial wavefunction. The exciton binding energies have been calculated as a function of external electric field for various well and barrier widths. The nonspherical trial wavefunction leads to a better estimate of the exciton binding energy, especially in high electric field, than that calculated with a spherical one. The calculations show that the binding energy is strongly dependent on the external electric fields: the variation (increase or decrease) is related to the spatial distribution of the wavefunctions. The results of the calculation are consistent with our experimental results.

Transmittance fluctuations and nonlinearity in random chains in the presence of applied electric fields.

We have carried out numerical investigations of transmittance fluctuations in disordered chains in the presence of external electric fields. We have obtained an almost constant fluctuation in a length scale smaller than the localization length. However, the value of the fluctuation in the plateau region is dependent on the external electric field and the strength of the disorder. We have also studied the transmittance autocorrelation as a function of external electric field to probe the nonlinearity in the transmittance.

Beam-coupling in tetragonal potassium Tantalate-Niobate crystals

Beam-coupling is investigated in a nominally pure tetragonal potassium Tantalate-Niobate (KTN) crystal as a function of external electric field, spatial frequency and light wavelength. The variation of these parameters leads to a change of the direction of energy transfer between the two recording beams. The experimental results can be consistently described by a one-center charge-transport model taking into account electron and hole contributions to photoconductivity and space-charge limitations due to the available trap density.

Thermoluminescence 155-161IN crystalline phenanthrene

Charge carrier photogeneration in crystalline phenanthrene has been studied by monitoring the UV-induced thermoluminescence (UVTL) as a function of external electric field for the excitation quanta at energies lower than the band gap. The electric field effect on the UVTL is discussed in terms of Poole-Frenkel- and Onsager-type dissociation of the defect-trapped geminate electron-hole pairs produced under low-temperature excitation. Quantitative agreement with the experiment is obtained with the Onsager-type model, indicating that the average distance between hole and electron in the trapped geminate pairs amounts to 7 nm.

Exciton motion under an external electric field in GaAs

The zero-phonon exciton line in GaAs has been investigated as a function of external electric field. The excitonic emission peak of the upper polariton branch shifted to higher photon energies when the external electric field was increased up to 20 V cm-1. Simultaneously, the electron temperature increased from 4.9K to 20K. Emission due to exciton-electron inelastic collision including lower polariton branch was also observed, showing the peak shift to lower photon energies. A model of the exciton motion and heating of the electron gas system has been proposed.

Comment on Plasmon Linewidth Experiments for Electrons on a Helium Surface

We show that the proper application of the established theory of electron-ripplon scattering for electrons trapped on helium correctly predicts the absolute linewidth, as a function of external electric field, observed in a recent plasmon experiment.